Calculating relative atomic mass

• What is the structure of an atom?

  An atom consists of a nucleus containing protons and neutrons, surrounded by electrons in shells.
• How can the numbers of subatomic particles in an atom be calculated?

  The numbers of subatomic particles can be calculated from its atomic number and mass number.
• What is the standard atom used for comparing the masses of other atoms?

  • The carbon-12 atom, \(_{6}^{12}\textrm{C}\)
• What is relative atomic mass?

  Relative atomic mass is the average mass of an atom compared to 1/12th the mass of a carbon-12 atom.
• How is the relative atomic mass, \(A_r\), of an element calculated?

  It is calculated from the mass numbers of its isotopes and their abundance.
• What is the mass number of an atom?

  The mass number is the number of protons and neutrons found in the nucleus of an atom.
• What does abundance refer to in the context of isotopes?

  Abundance refers to how much of a particular isotope exists compared to others.
• How many isotopes does chlorine naturally exist as?

  Chlorine naturally exists as two isotopes: chlorine-35 and chlorine-37.
• What are the abundances of chlorine-35 and chlorine-37?

  The abundance of chlorine-35 is 75% and chlorine-37 is 25%.
• How do you calculate the relative atomic mass of chlorine?

  Use the formula \(A_{r} = \frac{(75 \times 35)+(25 \times 37)}{(75+25)}\).
• What is the calculated relative atomic mass of chlorine?

  The relative atomic mass of chlorine is \(A_{r} = 35.5\) (to 1 decimal place).
• What are the mass numbers and abundances of the naturally occurring copper isotopes?

  Copper has mass numbers of 63 (69% abundance) and 65 (31% abundance).
• How do you calculate the relative atomic mass of copper?

  Use the formula \(A_{r} = \frac{(69 \times 63)+(31 \times 65)}{(69+31)}\).
• What is the calculated relative atomic mass of copper?

  The relative atomic mass of copper is \(A_{r} = 63.6\) (to 1 decimal place).
• What is the process for calculating relative atomic mass using isotopes and their abundances?

  1. Identify the mass numbers and abundances of the isotopes.
  2. Use the formula:

  \[

  A_{r} = \frac{(abundance_1 \times mass_1) + (abundance_2 \times mass_2)}{(abundance_1 + abundance_2)}

  \]

  1. Calculate the total mass and divide by the total number of atoms.